1. Field of the Invention
This invention relates to improved systems of drying ovens having associated means for heat reclamation and air pollution control and to methods of operating same. The ovens are primarily for drying or baking of paint or other coatings or pipes or the like where the emissions are primarily hydrocarbons.
2. Brief Description of the Prior Art
In pipe-coating operation, organic coatings are applied internally. In such operations, where progressive paint baking is involved, there are multiple ovens located in sequence. These ovens operate, in most cases, at different temperatures. The physical size of the ovens and the operating parameters differ according to the size of the pipe being coated. Conventional practice is to use fume incineration on the exhaust from each oven to oxidize the hydrocarbon emissions. A number of prior art patents disclose various arrangements for oxidative control of emissions from drying ovens.
Flynn U.S. Pat. No. 4,133,636 discloses an oven for treating web stock, especially a tentor for treating textile fabric, to remove volatile combustible substances therefrom. The oven employs a recycle circuit in which the temperature of the oven discharge gaseous stream is first raised by combustion of the volatilized substances therein, and then lowered by entry of cooler, supplemental air, after which part of the gaseous oven discharge gaseous stream is first raised by combustion of the volatilized substances therein, and then lowered by entry of cooler, supplemental air, after which part of the gaseous stream is returned to the oven and part used for pre-heating of stock or post-heating in other oven sections.
Wilkinson U.S. Pat. No. 3,437,321 discloses a paint-drying system in which the vapors of the volatile solvents are burned to eliminate pollution of the atmosphere and heating is reclaimed from such combustion.
Grieve U.S. Pat. No. 3,627,290 discloses an air pollution control system in which a stream of hot gas and air, exiting from a drying, baking, or curing oven, and containing pollutants is diverted through an incinerator, where the pollutants are burned to water and carbon dioxide. There is an intricate damper control system for regulating flow of gasses in accordance with oven temperature.
Jones U.S. Pat. No. 4,017,254 discloses a recirculating furnace-dryer combination including a combustion chamber, a housing surrounding the combustion chamber for maintaining a super-atmospheric pressure within the combustion chamber, dryer in which a super-atmospheric pressure may be maintained and a feed conduit through which the heated gasses may be supplied from the combustion chamber to the dryer. Return conduits recirculate exhaust gasses from the dryer for repressurization into the housing from which they are recirculated into the combustion chamber. The system is provided with temperature sensing devices and pressure sensing devices for control of flow of combustion and dryer gasses.
Phillips U.S. Pat. No. 4,092,100 discloses a drying oven for painted surfaces wherein the work is heated and dried by heated high pressure air blown against the work as it passes through the oven. The solvents stripped from the work are incinerated and the heat recovered from makeup heated air to the furnace.
These prior art patents suffer from the disadvantage that their systems are quite complicated, large in size, and quite expensive to build. In addition, in some cases, very intricate and expensive controls are required which add to the expense of the system.